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Research Papers

Optimum Performance of a Regenerative Gas Turbine Power Plant Operating With/Without a Solid Oxide Fuel Cell

[+] Author and Article Information
Y. Haseli

 Department of Mechanical Engineering, Eindhoven University of Technology, P. O. Box 513, Eindhoven 5600 MB, Eindhoven, The Netherlandsy.haseli@tue.nl

J. Fuel Cell Sci. Technol 8(5), 051003 (Jun 13, 2011) (9 pages) doi:10.1115/1.4003978 History: Received October 31, 2010; Revised March 09, 2011; Published June 13, 2011; Online June 13, 2011

Optimum pressure ratios of a regenerative gas turbine (RGT) power plant with and without a solid oxide fuel cell are investigated. It is shown that assuming a constant specific heat ratio throughout the RGT plant, explicit expressions can be derived for the optimum pressure ratios leading to maximum thermal efficiency and maximum net work output. It would be analytically complicated to apply the same method for the hybrid system due to the dependence of electrochemical parameters such as cell voltage on thermodynamic parameters like pressure and temperature. So, the thermodynamic optimization of this system is numerically studied using models of RGT plant and solid oxide fuel cell. Irreversibilities in terms of component efficiencies and total pressure drop within each configuration are taken into account. The main results for the RGT plant include maximization of the work output at the expenses of 2–4% lower thermal efficiency and higher capital costs of turbo-compressor compared to a design based on maximum thermal efficiency. On the other hand, the hybrid system is studied for a turbine inlet temperature (TIT) of 1 250–1 450 K and 10–20% total pressure drop in the system. The maximum thermal efficiency is found to be at a pressure ratio of 3–4, which is consistent with past studies. A higher TIT leads to a higher pressure ratio; however, no significant effect of pressure drop on the optimum pressure ratio is observed. The maximum work output of the hybrid system may take place at a pressure ratio at which the compressor outlet temperature is equal to the turbine downstream temperature. The work output increases with increasing the pressure ratio up to a point after which it starts to vary slightly. The pressure ratio at this point is suggested to be the optimal because the work output is very close to its maximum and the thermal efficiency is as high as a littler less than 60%.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic representation of a regenerative gas turbine

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Figure 2

Schematic representation of an integrated solid oxide fuel cell regenerative gas turbine power plant

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Figure 3

The effects of the temperature ratio and the pressure drop factor on (a) optimum pressure ratios leading to a maximum power output and a maximum efficiency represented by rp,w and rp,η respectively, (b) corresponding thermal efficiency, and (c) corresponding power output of a RGT plant

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Figure 4

The difference between the optimum pressure ratios obtained from two different criteria and the differences between the corresponding net works and the thermal efficiencies

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Figure 7

Variation of the fuel to air ratio with pressure ratio at three turbine inlet temperatures (RGT plant combined with a SOFC) – PF  = 0.85

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Figure 8

Relationship between the work output of a RGT plant combined with a SOFC and the effective temperature difference at three turbine inlet temperatures – PF  = 0.85

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Figure 9

Typical thermal efficiency–work output map at PF  = 0.85 for a RGT plant combined with a SOFC. Dashed lines represent constant pressure ratio.

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Figure 11

Thermal efficiency–work output map of a RGT plant combined with a SOFC at TIT = 1 250 K. Dashed lines represent constant pressure ratio.

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Figure 10

Variation of the thermal efficiency and the work output with pressure ratio at three values of the pressure drop factor (RGT plant combined with a SOFC) – TIT = 1 250 K

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Figure 12

Variation of the fuel to air ratio with pressure ratio at three values of pressure drop factor (RGT plant combined with a SOFC) – TIT = 1 250

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Figure 6

Variation of the thermal efficiency and the work output with pressure ratio at three turbine inlet temperatures (RGT plant combined with a SOFC) – PF  = 0.85

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Figure 5

The relationship between the work output and the effective temperature difference in a RGT plant at three values of the temperature ratio, T *

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